The long-recognized cold-induced activation and damage of human platelets has recently been shown to be associated with platelets passing through a thermotropic phase transition. This proposal has the long-term objective of developing mechanisms of stabilizing platelets during and after this damaging event, resulting in platelets being more tolerant of cold storage with greatly increased storage life time. Antifreeze glycoproteins (AFGPs) from the blood of certain polar fish are capable of preventing membrane leakage during passage through the phase transition. Recent work shows that AFGPs appear to stabilize platelets during chilling and storage below the phase transition temperature. The proposal seeks to better define the mechanisms involved in the cold storage lesion in platelets including the role of intracellular and extracellular calcium. The anticipated studies will also provide evidence as to whether AFGPs might inhibit temperature change associated events including inhibition of membrane leakage and lateral phase separation and/or phospholipase A2 (PLA2) activity. An array of techniques will be employed to accomplish these objectives. Among these is Fourier-transform infrared spectroscopy (FTIR). This will be used to monitor membrane phase transitions and lateral phase separation. Fluorescent phase spectroscopy will be employed for measuring internal calcium concentration, lateral phase separation, and PLA2 activity. Analytical thin layer chromatography (TLC) and gas chromatography will also be used to measure PLA2 activity and membrane composition. FACScanning will measure the expression of glycoproteins known to be on the platelet surface including GPs Ib and IIb/IIIa, and P-selectin. These will be measured in conjunction with aggregometry to quantify the level of activation and agonist responsiveness in human platelets during and after cold storage.